1. Field of the Invention
The present invention relates to a monolithic microwave integrated circuit (MMIC) which handles microwave or millimeter wave signals used in such applications as mobile communications, and more specifically to the achievement of a compact passive element circuit.
2. Description of Related Art
A monolithic microwave IC is formed by integrating onto a substrate of GaAs or the like transistors as an active element and passive elements such as spiral inductors, interdigital capacitors, MIM capacitors, transmission paths, and thin-film resistors.
In a monolithic microwave IC in the past, and particularly in a high-output monolithic microwave IC, one problem was that of how to achieve compactness and reduce losses in the input and output matching circuits. This was because of it not being possible to achieve a compact capacitor with high capacitance and because of the difficulty in reducing the loss in lines that form such elements as inductors.
FIG. 5 shows an example of a matching circuit of a monolithic microwave IC amplifier of the past. This includes a spiral inductor 501 and a thin-film capacitor 502 made from SiN.sub.x or the like, for the purpose of impedance matching. Because the use of thin-film capacitors to serve as large-capacitance capacitors between stages occupies a large part of the chip surface area and represents a hindrance to the achievement of compactness, the approach taken is that of providing this in the form of a chip capacitor 503 that is external to the monolithic microwave IC.
As indicated in the Japanese Unexamined Utility Model Publication No.03-21857, there has been a study made of a method to laminate a spiral inductor pattern on top of a capacitor after formation of an insulation film. As indicated in the Japanese Unexamined Patent Publication No.05-110311, there has been a study of a circuit in which a stripline or inductor is formed on a dielectric layer having a high dielectric coefficient over a dielectric layer having a lower dielectric coefficient.
The spiral inductor 501 that has been used is one in which, after the lead line 504 is formed using an electrode metal, an insulation film is deposited, over which metallic plating of the spiral part is done to implement the wiring.
However the above-noted configuration, in which a capacitor is provided external to the monolithic microwave IC, made it difficult to achieve a cost reduction by means of the adoption of an monolithic microwave IC. Also, the method of forming the above-noted inductor on top of an insulation film or on top of a dielectric layer involves a complex process, in addition to the problem of achieving low inductor loss.
With the above-noted inductor forming method, because of the high resistance of the lead, it is difficult to achieve an advantage in terms of lowered resistance by making the plating of the inductor part thick.
In view of the above-described drawbacks in the prior art, an object of the present invention is to provide a passive element circuit which features compactness and low loss, and which is also both simple and can be formed with good repeatability.